Skeletal System and Bone Development

These flashcards cover key concepts related to the skeletal system, bone cell types, bone formation processes, and fracture healing.

Osteogenic Cell

The stem cell that gives rise to most other bone cell types and is capable of undergoing mitosis.

Osteoblasts

Bone-forming cells that secrete bone matrix and cannot undergo mitosis once differentiated.

Osteocytes

Mature bone cells that were once osteoblasts, trapped in the bone matrix they secreted.

Osteoclasts

Bone-dissolving cells derived from white blood cells that resorb the extracellular matrix of bone.

Resorption

The process by which osteoclasts break down bone and release calcium and phosphate into the bloodstream.

Intramembranous Ossification

The ossification that produces flat bones of the skull and most of the clavicle.

Endochondral Ossification

The process of bone development that occurs from a pre-existing model composed of hyaline cartilage.

Hyaline Cartilage

A type of cartilage that serves as a model for bone in endochondral ossification.

Ossification Center

The area where bone tissue begins to form during ossification.

Calcification

The process where osteoblasts lay down the bone matrix and become trapped as osteocytes.

Trabeculae

The porous structure of spongy bone that develops within the bone.

Epiphyseal Plate

The growth plate allowing for the lengthening of bone, containing areas of active cartilage.

Hypertrophy

The increase in cell size that stimulates the surrounding extracellular matrix to calcify during bone development.

Primary Ossification Center

The initial site of bone formation in the middle of long bones during development.

Secondary Ossification Center

The area where bone formation occurs in the epiphyses, leading to the development of articular cartilage.

Fracture Healing

The process involving blood clot formation, soft and hard callus formation, followed by remodeling of bone.

Bone Remodeling

The lifelong process by which bone is constantly renewed by the work of osteoblasts and osteoclasts.

Step 1.) Condesation of Mesenchyme (soft tissue clumps): Mesenchymal (embryonic connective tissue) condenses into a soft sheet-like structure where bone will form.

Step 2.) Formation of Ossification Centers: A center for bone formation appears in this soft tissue. Blood vessels grow into the area.

Step 3.) Calcification (harding begins): Osteogenic cells become osteoblasts. Osteoblasts start laying down bone material. As they get trapped they become osteocytes, living in lacunae and forming canaliculi. This material hardens, forming early bone.

Step 4.) Formation of Trabeculae (Spongy bone forms): Hardened pieces of trabecular (bone) create spongy bone (which looks like honeycomb). Blood vessels weave through this network.

Step 5.) Development of the Periosteum (Compact bone and covering): Osteoblast on the surface keep laying down material, creating a layer of compact (dense) bone. The periosteum (a tough outer covering) forms around the bone. It has osteogenic cells that make new osteoblasts for ongoing bone formation.